I have an imperfect solution depending on the properties of the cell contents. It is valid for all inner borders and the left outer border. It does not work if you want to tag the right border of the table.
You must know the width of the character/image (w) and the left padding space to contents from
Anchor the character/image to the paragraph in a cell. Adjust position as follows:
From left to
Paragraph area by -( w/2 + p) to center it exactly over the left cell border
Paragraph text area
With these settings, I can add/remove columns and the tag mark remains in the correct position as long as I don’t suppress the anchoring cell.
The trick does not work well if there are several paragraphs in the marking cell. You must attach the mark the paragraph nearest the center. To improve centering, select center vertical alignment of cell contents.
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